DESCRIPTION (Applicant's Abstract): In the microenvironment of the human gut epithelium, armed effector T cells (T-IELs) with cytolytic functions are tightly regulated by CD94/NKG2, a novel family of HLA-E specific heterodimeric receptors originally identified on NK cells. These receptors can switch adaptive responses on and off by using different activating or inhibitory NKG2 isotypes and appear to regulate remarkably large T-IEL clonal expansions in healthy individuals. In celiac disease, a condition associated with epithelial damage, they exclusively express activating isotypes, suggesting that dysregulation causes disease. The overarching goal of the proposed research is to develop a model of how adaptive immunity mediated by cytolytic effector T cells is regulated in the gut microenvironment by CD94/NKG2 receptors of innate immunity. The investigator will focus on three specific aims fundamental to understanding the biological significance of this regulatory system. In Specific Aim 1, expression and regulation of HLA-E and G on intestinal epithelial cells, cytokines produced in the GALT in normal and inflammatory conditions will be used to stimulate expression of HLA-E and G by freshly isolated IECs, IEC lines and professional APCs. In Specific Aim 2, expression and regulation of CD94/NKG2 isotypes by T-IELs, the investigator will characterize the pattern of expression of the different CD94/NKG2 isotypes, the TCR V-beta and V-alpha repertoire of T-IELs expressing distinct CD94/NKG2 isotypes (by spectroanalysis and sequencing), and the cytokine profile of T-IELs expressing distinct CD94/NKG2 isotypes. In Specific Aim 3, functional properties of CD94INKG2 receptors expressed by T-IELs, cloned T-IELs expressing single NKG2 isotypes will be used to determine how they contribute to cytolytic function and cytokine secretion and to characterize the biochemical signals involved. The proposed research will test in a molecularly well-defined system the general hypothesis that NK receptors and non-classical MHC class I-like molecules regulate interactions between T-IELs and intestinal epithelial cells. The results are likely to have important implications for our understanding of the processes that fine tune cytolytic T cell responses in the high antigen environment of the gut, regulating local immunity and controlling epithelial cell damage.